There are two parts to this: prying up the lid, and opening the coffin inside.
If you click on the lid, Nancy will tell you that the lid is way too heavy, but she thinks she could pry it off if she had some sort of lever. What you need is some long, strong pipe or board or something that will fit into that little hole on the left side. Can you find anything like that?
If you walk up to the coffin and then turn around, you'll see a bundle of spears leaning against the left wall. That looks ideal.
Well, almost; Nancy says it's not quite strong enough. You need one more piece to add to the spears, and you'll be set. Say, what was that noise?
When you tried to pry off the lid, there was a loud crash from the main room. Let's go look into that.
Turns out the scaffolding around Abdullah collapsed ... luckily, just enough to make a loud noise but not enough to hurt him. Oh, and to reduce the scaffolding to a pile of boards and pipes. How convenient!
Grab a "strong board" from the pile of scaffolding pieces on the right of Abdullah, then take it back to the tomb and put it and the spears into the hole in the sarcophagus. Voila! And inside we find --